/**
 * covert canvas to image
 * and save the image file
 */

var Canvas2Image = (function () {
  // check if support sth.
  var $support = (function () {
    var canvas = document.createElement('canvas'),
      ctx = canvas.getContext('2d')

    return {
      canvas: !!ctx,
      imageData: !!ctx.getImageData,
      dataURL: !!canvas.toDataURL,
      btoa: !!window.btoa,
    }
  })()

  var downloadMime = 'image/octet-stream'

  function scaleCanvas(canvas, width, height) {
    var w = canvas.width,
      h = canvas.height
    if (width == undefined) {
      width = w
    }
    if (height == undefined) {
      height = h
    }

    var retCanvas = document.createElement('canvas')
    var retCtx = retCanvas.getContext('2d')
    retCanvas.width = width
    retCanvas.height = height
    retCtx.drawImage(canvas, 0, 0, w, h, 0, 0, width, height)
    return retCanvas
  }

  function getDataURL(canvas, type, width, height) {
    canvas = scaleCanvas(canvas, width, height)
    return canvas.toDataURL(type)
  }

  function saveFile(strData) {
    document.location.href = strData
  }

  function genImage(strData) {
    var img = document.createElement('img')
    img.src = strData
    return img
  }
  function fixType(type) {
    type = type.toLowerCase().replace(/jpg/i, 'jpeg')
    var r = type.match(/png|jpeg|bmp|gif/)[0]
    return 'image/' + r
  }
  function encodeData(data) {
    if (!window.btoa) {
      throw 'btoa undefined'
    }
    var str = ''
    if (typeof data == 'string') {
      str = data
    } else {
      for (var i = 0; i < data.length; i++) {
        str += String.fromCharCode(data[i])
      }
    }

    return btoa(str)
  }
  function getImageData(canvas) {
    var w = canvas.width,
      h = canvas.height
    return canvas.getContext('2d').getImageData(0, 0, w, h)
  }
  function makeURI(strData, type) {
    return 'data:' + type + ';base64,' + strData
  }

  /**
   * create bitmap image
   * 按照规则生成图片响应头和响应体
   */
  var genBitmapImage = function (oData) {
    //
    // BITMAPFILEHEADER: http://msdn.microsoft.com/en-us/library/windows/desktop/dd183374(v=vs.85).aspx
    // BITMAPINFOHEADER: http://msdn.microsoft.com/en-us/library/dd183376.aspx
    //

    var biWidth = oData.width
    var biHeight = oData.height
    var biSizeImage = biWidth * biHeight * 3
    var bfSize = biSizeImage + 54 // total header size = 54 bytes

    //
    //  typedef struct tagBITMAPFILEHEADER {
    //  	WORD bfType;
    //  	DWORD bfSize;
    //  	WORD bfReserved1;
    //  	WORD bfReserved2;
    //  	DWORD bfOffBits;
    //  } BITMAPFILEHEADER;
    //
    var BITMAPFILEHEADER = [
      // WORD bfType -- The file type signature; must be "BM"
      0x42,
      0x4d,
      // DWORD bfSize -- The size, in bytes, of the bitmap file
      bfSize & 0xff,
      (bfSize >> 8) & 0xff,
      (bfSize >> 16) & 0xff,
      (bfSize >> 24) & 0xff,
      // WORD bfReserved1 -- Reserved; must be zero
      0,
      0,
      // WORD bfReserved2 -- Reserved; must be zero
      0,
      0,
      // DWORD bfOffBits -- The offset, in bytes, from the beginning of the BITMAPFILEHEADER structure to the bitmap bits.
      54,
      0,
      0,
      0,
    ]

    //
    //  typedef struct tagBITMAPINFOHEADER {
    //  	DWORD biSize;
    //  	LONG  biWidth;
    //  	LONG  biHeight;
    //  	WORD  biPlanes;
    //  	WORD  biBitCount;
    //  	DWORD biCompression;
    //  	DWORD biSizeImage;
    //  	LONG  biXPelsPerMeter;
    //  	LONG  biYPelsPerMeter;
    //  	DWORD biClrUsed;
    //  	DWORD biClrImportant;
    //  } BITMAPINFOHEADER, *PBITMAPINFOHEADER;
    //
    var BITMAPINFOHEADER = [
      // DWORD biSize -- The number of bytes required by the structure
      40,
      0,
      0,
      0,
      // LONG biWidth -- The width of the bitmap, in pixels
      biWidth & 0xff,
      (biWidth >> 8) & 0xff,
      (biWidth >> 16) & 0xff,
      (biWidth >> 24) & 0xff,
      // LONG biHeight -- The height of the bitmap, in pixels
      biHeight & 0xff,
      (biHeight >> 8) & 0xff,
      (biHeight >> 16) & 0xff,
      (biHeight >> 24) & 0xff,
      // WORD biPlanes -- The number of planes for the target device. This value must be set to 1
      1,
      0,
      // WORD biBitCount -- The number of bits-per-pixel, 24 bits-per-pixel -- the bitmap
      // has a maximum of 2^24 colors (16777216, Truecolor)
      24,
      0,
      // DWORD biCompression -- The type of compression, BI_RGB (code 0) -- uncompressed
      0,
      0,
      0,
      0,
      // DWORD biSizeImage -- The size, in bytes, of the image. This may be set to zero for BI_RGB bitmaps
      biSizeImage & 0xff,
      (biSizeImage >> 8) & 0xff,
      (biSizeImage >> 16) & 0xff,
      (biSizeImage >> 24) & 0xff,
      // LONG biXPelsPerMeter, unused
      0,
      0,
      0,
      0,
      // LONG biYPelsPerMeter, unused
      0,
      0,
      0,
      0,
      // DWORD biClrUsed, the number of color indexes of palette, unused
      0,
      0,
      0,
      0,
      // DWORD biClrImportant, unused
      0,
      0,
      0,
      0,
    ]

    var iPadding = (4 - ((biWidth * 3) % 4)) % 4

    var aImgData = oData.data

    var strPixelData = ''
    var biWidth4 = biWidth << 2
    var y = biHeight
    var fromCharCode = String.fromCharCode

    do {
      var iOffsetY = biWidth4 * (y - 1)
      var strPixelRow = ''
      for (var x = 0; x < biWidth; x++) {
        var iOffsetX = x << 2
        strPixelRow +=
          fromCharCode(aImgData[iOffsetY + iOffsetX + 2]) +
          fromCharCode(aImgData[iOffsetY + iOffsetX + 1]) +
          fromCharCode(aImgData[iOffsetY + iOffsetX])
      }

      for (var c = 0; c < iPadding; c++) {
        strPixelRow += String.fromCharCode(0)
      }

      strPixelData += strPixelRow
    } while (--y)

    var strEncoded =
      encodeData(BITMAPFILEHEADER.concat(BITMAPINFOHEADER)) +
      encodeData(strPixelData)

    return strEncoded
  }

  /**
   * saveAsImage
   * @param canvasElement
   * @param {String} image type
   * @param {Number} [optional] png width
   * @param {Number} [optional] png height
   */
  var saveAsImage = function (canvas, width, height, type) {
    if ($support.canvas && $support.dataURL) {
      if (typeof canvas == 'string') {
        canvas = document.getElementById(canvas)
      }
      if (type == undefined) {
        type = 'png'
      }
      type = fixType(type)
      if (/bmp/.test(type)) {
        var data = getImageData(scaleCanvas(canvas, width, height))
        let strData = genBitmapImage(data)
        saveFile(makeURI(strData, downloadMime))
      } else {
        let strData = getDataURL(canvas, type, width, height)
        saveFile(strData.replace(type, downloadMime))
      }
    }
  }

  var convertToImage = function (canvas, width, height, type) {
    if ($support.canvas && $support.dataURL) {
      if (typeof canvas == 'string') {
        canvas = document.getElementById(canvas)
      }
      if (type == undefined) {
        type = 'png'
      }
      type = fixType(type)

      if (/bmp/.test(type)) {
        var data = getImageData(scaleCanvas(canvas, width, height))
        let strData = genBitmapImage(data)
        return genImage(makeURI(strData, 'image/bmp'))
      } else {
        let strData = getDataURL(canvas, type, width, height)
        return genImage(strData)
      }
    }
  }

  return {
    saveAsImage: saveAsImage,
    saveAsPNG: function (canvas, width, height) {
      return saveAsImage(canvas, width, height, 'png')
    },
    saveAsJPEG: function (canvas, width, height) {
      return saveAsImage(canvas, width, height, 'jpeg')
    },
    saveAsGIF: function (canvas, width, height) {
      return saveAsImage(canvas, width, height, 'gif')
    },
    saveAsBMP: function (canvas, width, height) {
      return saveAsImage(canvas, width, height, 'bmp')
    },

    convertToImage: convertToImage,
    convertToPNG: function (canvas, width, height) {
      return convertToImage(canvas, width, height, 'png')
    },
    convertToJPEG: function (canvas, width, height) {
      return convertToImage(canvas, width, height, 'jpeg')
    },
    convertToGIF: function (canvas, width, height) {
      return convertToImage(canvas, width, height, 'gif')
    },
    convertToBMP: function (canvas, width, height) {
      return convertToImage(canvas, width, height, 'bmp')
    },
  }
})()
export default Canvas2Image
